Method and system for television communication



2 sheetsf-sheet 1 H. G. MILLER Filed Aug'. 2.' 19.59

EN' M June l0, 1941.

METHOD AND SYSTEM FOR TELEVISION COMMUNICATION `lune 10,1941. H G, MILLER METHOD AND SYSTEM FOR TELEVISION COMMUNICATION Filed Aug. 2. 1939 2 Shee'rLs-Sheet 2 INVENTOR named Julie 1o, 1941 UNITI-3Dv STATES PATENT OFFICE" METHOD AND SYSTEM FOB TELEVISION COMMUNICATION Y Home G. Miner, Beueviue, N. J., mignon to Auen B. Du Mont Laboratories, Inc., Pa'ual'c, N. J., a corporation o! New Jersey Application August 2, 1939,

6 Claims.

- enough either required a relatively large number of tubes, or produced unstable results. That is, one or more of the following undesirable actions were found to be present. 'I he synchronizing action varied widely with the instantaneous background level of the composite video signal, so that serial no. 287,940 f (Cl. P18-7.5)

above-mentioned sources of instability and producs strong, steady synchronizing withv excellent interlace under widely varying conditions.

a sudden change of scene caused a disagreeable jump in all or part of the reproduced picture raster, or even caused .temporary loss of synchronization. Power supply surges affected the synchronization, causing-undesired motion or temporary loss of synchronism in the reproduced raster. Conduction currents in the input/ circuit of the synchronizing separator tube or tubes produced distortion of the composite video signal waveform, causing non-uniform horizontal synchronism and some times variable interlace or loss of vertical synchronism. Some of the pic- .ture portion of the composite video signal occasionally passed through the synchronizing septerlace. Poor amplitude discrimination in one or both separators allowed the blanking signals to be transmitted through/the separator, causing variable interlace and/or ragged horizontal synchronizing.

With the foregoing in mind, it is one ofthe.

objects of my invention to Aprovide an improved method and system for television communication which eliminates or greatly reduces the Other objects and advantages will hereinafter For fthe purpose of illustrating my invention, an embodiment thereof is shown in the drawings, wherein' s Figure`1 is a simplified, diagrammatic showing oi a television receiving system constructedand operating in accordance with my invention; and

Fig. 2 is a view similar to Fig. 1, showing a modification. l

With reference to Fig. 1, the-numeral I0 designates a conventional receiver for video signals and horizontal and vertical synchronizing pulses. This composite signal is taken fromthe output circuit di the second detector tube I I and ampliiled by the video amplifier tube l2. From the output of the tube I2, the composite video signal is applied as shown, atfhigh level, to the grid Il of a scanning device I5 in the'form of a conventional cathode-ray tube.

The composite signal, comprising the video signals and the horizontal and vertical synchronizing pulses, is also taken from the output of the video ampliiier tube I2, atv high level, and applied through a large condenser I6 and a large resistor I1 to the respective cathodes I8 and I9 of the separator tubes 20 and 2l. The separator cathodes I8 and I9 are therefore automatically ybiased to nominalcutoif potential, and only the negative, horizontal and verticalv synchronizing peaks of .the composite signal get through the separator means.

The respective grids 22 and 23 of the separator tubes A are connected through the low-pass filter shownf'to the same point 24 as t-he cathodes IB and I0 are driven from.

In operation, the video signal does not reach the grids 22 and 23, but any low-frequency surges of whatever origin arriving at .the condenser IO are transmitted to the grids 22 and 23 as well as to the cathodes I8 and I9. Y Thus, such undesirable 'surges cancel out in the-separator tubes and accordingly do not get .through the same or anect the separator action. The lowpass lter may take the form shown in Fig. 1, in

ipulses from the separator tubes 20 and 2|, re-

spectively, may be fed to horizontal and vertical sweep oscillator tubes 29 and 30, respectively. The output of the sweep oscillator tubes 29 and 3o may be applied, as represented, to drive the respective, local, horizontal and vertical sweepcircuits 3| and 32 for saw-tooth deflection of the scanning electron ray 33 by the respective plates 3B and 35. The transmitted scene or picture is thereby reproduced on the fluorescent screen 36 in the well-known manner. n

The value of resistor I1 is rather criticalin order to obtain proper cutoff and large Synchronizing output from the separator tubes 20 and 2i under widely varying signal-level conditions. A value of Yabout 50,000 ohms for resistor I1 has been found to be suitable for use with average triode tubes.

As an alternative. the low-pass filter might be omitted, and the grids 22 and 23 of the separator tubes connecteddirectly to the low-potential end 31 of resistor I1. It has been found, however, that such an arrangement does not provide as good stability in the separator tubes.

From the foregoing, it will be seen that in my improved method and system, a composite video signal of the maximum amplitude available anywhere in the video amplifier, is applied :to the separator input circuit. That is, the signals are taken from the output of .the video amplifier, at high level, and applied in the novel manner shown to the cathodes I8 and I9 and the grids 22 and 23 of the separator tubes.

In the modification shown in Fig. 2, the various parts or elements corresponding to and serving the same purpose as the respective parts or.

elements in Fig. l, have been designated by the same respective reference numerals as the latter. In Fig. 2, the separator tubes 20 and 2-I are shown as pento'des rather than as triodes, simply to illustrate the flexibility of my improved method and system. The condenser I5 and resistor I1 serve to transmit the composite video signals to the separator cathodes, as in Fig. 1. Condenser I6 and resistor I1 transmit all frequencies down to say one cycle per second. In Fig. 2, however, the source of the extraneous and undesirable low-frequency surges is assumed to be local, that is, within the circuits of the receiver. Such surges are cancelled out or rendered void in theirleffect on the separator tubes and 2i by applying them to the separator grids 22 and 23 through an attenuator or voltage divider, as shown.

A small condenser 38 operates to prevent highfrequency voltages from building up on theV separator grids 22 and 23.

In Fig. 2, resistor I1 should be large in comparison to resistor 39, resistor 4U should be large in comparison to resistor 4I, and resistor 4I should be large in comparison to resistor 42. Also, the product of resistor I1 and condenser I6 should 'be approximately equal to the product of resistor 40 and condenser 43. Under these conditions, cancellation of internally-generated disturbances is obtained when the quotient obtained by dividing the value of resistor 4I by the sum of the respective values lof resistors M and 4I equals the difference between unity and the product of G and the Value of resistor 39, where G is the screen-to-plate transconductance of the video amplifier I2. If the video amplifier I2 is a triode tube, G becomes zero and the value of resistor 44 becomes zero. Under conditions ordinarily met with in practice, the product of G and the value of resistor 39 is less than unity.

While my invention has been described more in connection with television communication, it will be selen that it has a broader application, and might be used in connection with facsimile apparatus, telephone or telegraph apparatus, or in fact in any case where a separation of different 'signals and electrical surges is desirable.

In the drawings, the various values of resistance, conductance and'capacity have been given by way of example, and may be varied to suit particular requirements. Furthermore, it will be understood that modifications within the conception of those skilled in the art are possible without departing from the spirit of my invention or the scope of the claims.

I claim as my invention:

1. In the art of television communication, the

, method of operation which comprises transmitting video signal and synchronizing signal together as a composite signal, applying the composite signal to an input circuit of separator means and in such manner that only,the negative peaks of the composite signal get through said separator means by Way of said input circuit, and applying to another input circuit of said separator means only undesirable electrical surges which occur and which are simultaneously applied with the composite signal on said firstnamed input circuit whereby such surges applied simultaneously to said input circuits cancel out and are accordingly prevented from getting through said separator means.

2. In a system for amplifying and separating signals of relatively high frequency from electrical surges of relatively low frequency, an amplifier for the high-frequency signals and the lowfrequency surges, separator means comprising an electron tube having a cathode and a grid, connecting means for applying both the amplified high-frequency signals and the amplified lowi'requency surges from the output circuit of said. amplifier to said cathode, and connecting means for applying only the amplified low-frequency surges from the output circuit of said amplifier to said grid whereby such surges cancel out Within the separator tube itself causing only the amplified signals of relatively high frequency' to appear in the output circuit of said tube.

3. In a picture-transmission system, means for amplifying video signals and synchronizing signais and electrical surges of relatively low frequency as compared to the frequency of the synchronizing signals, a scanning device for picture-reproduction, connecting means for applying the video signals to said device from` the output circuit of said amplifying means, separator means comprising an electron tube having a cathode and a grid, connecting means for applying both the amplified symchronizing signals and the amplified low-frequency surges from the output circuit of said amplifying means to said cathode, connecting means for applying only the amplified low-frequency surges from the output circuit of said amplifying means to said grid whereby such surges cancel out within the sepa.- rator tube itself causing only the amplified synchronizing signals of relatively high frequency to appear in the output circuit of said tube, and means controlled from the output ,circuit of said tube for governing scanning, action of said device.

4. In a television system, means for amplifying video signals and synchronizing signals and electrical surges of relatively low frequency as compared to the frequency ofthe synchronizing signals, a cathode-ray tube for picture-reprothe amplied low-frequency surges from the output circuit; of said amplifying means to said tively low frequency as compared to the frequency of the horizontal synchronizing signals, a cathode-ray tube for picture reproduction. connecting means for applying the video signals from the output circuit of said amplifying means to an electrode of said tube, separator means comprising a pair of electron tubes each having a cathode and a grid, connecting means for applying both the amplified synchronizing signals and the s amplified low-frequency surges from the output cathode, connecting means for applying only the circuit of said amplifying means to said cathodes, connecting means for applying only the amplied low-frequency surges from the output circuit of said amplifying means to said grids whereby such surges cancel out within the separator tubes causing only the amplified horizontal and vertical synchronizing signals to appear in the respective output circuits of said separator tubes, and means controlled from the output circuits of said separate tubes for causing simultaneous horizontal and vertical deflection oi the scanning electron ray of said first-named tube.

6. In a system for amplifying and separating signals of relatively high frequency from electrical surges of relatively low frequency. an amplifier for the high-frequency signals and the lowfrequency surges. separator means comprising a pair of electron tubes each having a cathode and a grid, connecting means for applying both the amplified high-frequency signals and the amplined low-frequency surges from the output circuit of said amplier to said cathodes, and connecting means for applying only the amplified low-frequency surges from the output circuit of said amplifier to said grids whereby such surges cancel out within the separator tubes causing only the amplied signals of relativelyhigh frequency to appear in the output circuits of said tubes.

HORACE G. MILLER. 

